Controller of vacuum pump

ABSTRACT

A vacuum pump has a pump mechanism section that performs evacuation to set a space to be evacuated to a predetermined degree of vacuum and an electric motor section for driving the pump mechanism section. A controller of the vacuum pump executes deceleration control to decrease a rotational speed of the electric motor section when an increase in load torque of the vacuum pump per unit time abruptly changes upward.

BACKGROUND OF THE INVENTION

The present invention relates to a controller of a vacuum pump having apump mechanism section that performs evacuation to set a space to beevacuated to a predetermined degree of vacuum, and an electric motorsection for driving the pump mechanism section.

There is known a semiconductor production apparatus of a type that has aload-lock chamber provided side-by-side with respect to a processchamber that performs film deposition and other processes to a wafer(substrate) as described in, for example, Japanese Patent Laid-OpenPublication No. 9-306972.

This apparatus performs wafer exchange between the process chamber andthe semiconductor production apparatus exterior via the load-lockchamber. A vacuum pump that sets the load-lock chamber to apredetermined degree of vacuum is connected via a valve to the load-lockchamber. This valve is designed in such a way as to be able to connector disconnect the load-lock chamber to or from the vacuum pump in termsof pressure when it is externally manipulated.

Wafer exchange between the load-lock chamber and the process chamber iscarried out under a state where the load-lock chamber is disconnectedfrom the semiconductor production apparatus exterior in terms ofpressure, and is set to a predetermined degree of vacuum by the vacuumpump. Wafer exchange between the load-lock chamber and the semiconductorproduction apparatus, on the other hand, is carried out under a statewhere the load-lock chamber is disconnected from the process chamber interms of pressure and is set back to the atmospheric pressure.

Work efficiency in semiconductor production is improved by performingfilm deposition and other processes in the process chamber disconnectedfrom the load-lock chamber in terms of pressure while wafer exchangebetween the load-lock chamber and the semiconductor production apparatusexterior is executed.

At the time of depressurizing the load-lock chamber under atmosphericpressure to a predetermined degree of vacuum again, the load-lockchamber is connected to the vacuum pump by setting the valve to an openstate from the closed state and then the load-lock chamber is evacuated.At this time, in the case where the valve is switched to the open statefrom the closed state while the vacuum pump is driven, the pressure inthe vacuum pump suddenly increases to atmospheric pressure from thepredetermined degree of vacuum, abruptly increasing the pressure load(pressure load associated with evacuation) of the vacuum pump. When anelectric motor is used as the drive source for the vacuum pump, theabrupt increase in pressure load quickly increases the output torque ofthe electric motor or the load torque of the vacuum pump.

One way to prevent the components of the vacuum pump from being damagedby the sudden increase in load torque of the vacuum pump is to controlthe electric motor using a controller in such a way that the load torqueof the vacuum pump does not exceed a predetermined upper limit. The timecharts in FIGS. 2(a) and 2(b) show examples of the mode of the control.A broken line 91 in FIG. 2(a) indicates the drive frequency when asynchronous motor type brushless motor is used as the electric motor. Abroken line 92 in FIG. 2(b) indicates the value of a current supplied tothe electric motor. The current value correlates with the size of theoutput torque of the electric motor section or the load torque of thevacuum pump.

When the valve is switched to the open state from the closed state attime t1, as shown in FIGS. 2(a) and 2(b), the abrupt increase inpressure load of the vacuum pump caused by the switching rapidlyincreases the value of the current supplied to the electric motor. Thatis, the load torque of the vacuum pump rapidly increases.

When the controller determines that the current value of the electricmotor has reached a predetermined upper limit i2 at time t2, it rapidlyreduces the drive frequency of the electric motor toward a drivefrequency fmin on the low-speed side of the rotational speed of theelectric motor from a drive frequency fmax on the high-speed side. Thereduction in drive frequency lowers the rotational speed of the electricmotor, thereby suppressing an increase in pressure load of the vacuumpump. This restricts the output torque of the electric motor or the loadtorque of the vacuum pump so that the torque does not exceed apredetermined upper limit, i.e., the upper limit of a torquecorresponding to the upper limit i2 of the supply current.

Although the aforementioned control mode prevents the components of thevacuum pump from being damaged by an excess increase in load torque ofthe vacuum pump, a rapid rise in load torque occurs when the closedstate of the valve is switched to the open state. At this time, anincreased speed in load torque differs significantly between the beforeand after time t1 at which the rise has started, i.e., an abrupt upwardchange in the increased speed of the load torque, and the state at whichthe increased speed is great, continues until the current value of theelectric motor reaches the predetermined upper limit i2.

Even if the control mode prevents an excess increase in load torque ofthe vacuum pump, therefore, the components of the vacuum pump may beshocked significantly by an abrupt upward change in the increased speedof the load torque or continuation of the state at which the increasedspeed is great after the upward change. This causes the components ofthe vacuum pump to be damaged.

To prevent the components of the vacuum pump from being damaged, thecomponents may be reinforced to be stronger. This however, undesirablyleads to enlargement and weight increase of the vacuum pump.

Accordingly, it is an object of the present invention to provide acontroller of a vacuum pump that can improve the durability of thevacuum pump without size enlargement or weight increase that mayoriginate from reinforcement of the vacuum pump.

SUMMARY OF THE INVENTION

To achieve the objects, according to one aspect of the invention, thereis provided a controller of a vacuum pump, which performs decelerationcontrol to decrease the rotational speed of an electric motor sectionwhen an increase in load torque of the vacuum pump per unit timeabruptly changes upward.

In the case where with the vacuum pump activating, the outside air isled into the space to be evacuated so that the pressure in the spacerapidly rises, for example, as the pressure torque of the vacuum pump(pressure load associated with evacuation) increases, the output torqueof the electric motor section, i.e., the load torque of the vacuum pumptends to rise. In this case, the increase in load torque of the vacuumpump per unit time (increased speed of the load torque of the vacuumpump) may change upward from the state where it is nearly zero to thestate where it exceeds a certain level. In other words, the increase inload torque of the vacuum pump per unit time may rapidly change upward.

The controller of the present invention performs deceleration control todecrease the rotational speed of the electric motor section when anincrease in load torque of the vacuum pump per unit time abruptlychanges upward. This reduces shocks applied to the components of thevacuum pump by the abrupt upward change in the increase in load torqueof the vacuum pump per unit time or the continuous state where theincrease in load torque of the vacuum pump per unit time is large afterthe upward change of the load torque when the load torque rises. It istherefore unnecessary to reinforce the components of the vacuum pump inorder to improve the shock resistance, thereby preventing areinforcement-originated size increase or weight increase of the vacuumpump.

According to this aspect of the invention, it is possible to moreaccurately grasp how much the increase in load torque of the vacuum pumpper unit time has changed in a predetermined time, as compared with themode that carries out deceleration control based on the increase in loadtorque of the vacuum pump per unit time. In this specification, the“rate of change in the increase in load torque of the vacuum pump perunit time” represents how much the increase in load torque of the vacuumpump per unit time has changed per unit time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a semiconductor production apparatusand a vacuum pump;

FIG. 2(a) is a time chart showing the drive frequency in an electricmotor section and FIG. 2(b) is a time chart showing the current value inthe electric motor section; and

FIGS. 3(a) and 3(b) show time charts in another embodiment, FIG. 3(a)being a time chart showing the drive frequency in an electric motorsection, while FIG. 3(b) is a time chart showing the current value inthe electric motor section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the invention as embodied in a vacuum pump forevacuating a load-lock chamber in a semiconductor production apparatusis described below with reference to the accompanying drawings.

As shown in FIG. 1, a process chamber 12 is provided side-by-side withrespect to a load-lock chamber 13 in a semiconductor productionapparatus 11. Deposition processes, such as vacuum deposition orsputtering on a wafer, are carried out in the process chamber 12. Thoseprocesses are executed after the process chamber 12 is set to apredetermined degree of vacuum by using an unillustrated evacuationsystem.

Wafer exchange between the exterior (atmospheric pressure space) of thesemiconductor production apparatus 11 and the process chamber 12 iscarried out via the load-lock chamber 13. That is, a passage forexchanging a wafer at the time of wafer exchange is provided betweenboth chambers 12 and 13 and a gate valve 14 that connects anddisconnects both chambers 12 and 13 to and from each other in terms ofpressure is provided in that passage. Further, the semiconductorproduction apparatus 11 is provided with a passage for wafer exchangebetween the load-lock chamber 13 and the exterior of the semiconductorproduction apparatus 11, and a gate valve 15 that connects anddisconnects the load-lock chamber 13 and the exterior to and from eachother in terms of pressure is provided in that passage.

A vacuum pump 20 is connected to the semiconductor production apparatus11 via an exhaust passage 16. The vacuum pump 20 evacuates the load-lockchamber 13 as a space to be evacuated. A first valve 17, which connectsand disconnects the load-lock chamber 13 and the vacuum pump 20 to andfrom each other in terms of pressure when manipulated externally, isprovided in the exhaust passage 16.

The load-lock chamber 13 is communicated with the exterior of thesemiconductor production apparatus 11 via an outside-air inlet passage18. A second valve 19, which can connect and disconnect the load-lockchamber 13 and the exterior to and from each other in terms of pressurewhen manipulated externally, is provided in the outside-air inletpassage 18.

The vacuum pump 20 has a pump mechanism section 21 that evacuates theload-lock chamber 13 to set the chamber 13 to a predetermined degree ofvacuum and an electric motor section 22 for driving the pump mechanismsection 21. The electric motor section 22 is comprised of a synchronousmotor type brushless motor, specifically a brushless DC motor, and isdriven by power supplied from an inverter 30 that constitutes thecontroller. The rotational speed of the electric motor section 22 isadjusted by adjusting the drive frequency (rotational-speed instructionvalue) in the supply current from the inverter 30.

In this embodiment, the electric motor section 22 is driven by a steadyvoltage by the inverter 30 and the value of the supply current to theelectric motor section 22 correlates with the magnitude of the outputtorque of the electric motor section 22, i.e., the load torque of thevacuum pump 20.

The inverter 30 has an electronic control unit (ECU) 31 equipped with amicrocomputer and a current detector 32. The ECU 31 and the currentdetector 32 constitute motor control means. The current detector 32detects the value of the supply current to the electric motor section 22and provides the ECU 31 with the detected information. The currentdetector 32 constitutes detection means that detects the value of thesupply current to the electric motor section 2. The ECU 31 adjusts thedrive frequency in the supply current to the electric motor section 22based on the detected information provided by the current detector 32.

The ECU 31 computes the output torque of the electric motor section 22or the load torque of the vacuum pump 20 based on the detectedinformation from the current detector 32, i.e., the value of the supplycurrent to the electric motor section 22. Based on the load torque, theECU 31 computes an increase in load torque of the vacuum pump 20 perunit time (which hereinafter is referred to as the increased speed ofthe load torque of the vacuum pump 20 for the sake of convenience). TheECU 31 repeatedly monitors the increased speed of the load torque of thevacuum pump 20 at a predetermined time interval.

When the ECU 31 determines that the increased speed of the load torqueof the vacuum pump 20 is greater than a predetermined value, the ECU 31determines that there has been an abrupt upward change in the increasedspeed of the load torque of the vacuum pump 20. Having made thisdecision, the ECU 31 changes the drive frequency in the supply currentto the electric motor section 22 to the low-speed side of the rotationalspeed of the electric motor section 22, i.e., reduces the drivefrequency, in order to decrease the increased speed of the load torqueof the vacuum pump 20. This control is referred to as decelerationcontrol.

The ECU 31 keeps monitoring the increased speed of the load torque ofthe vacuum pump 20 even after it has decided that the increased speed ofthe load torque of the vacuum pump 20 abruptly changed upward. Morespecifically, the ECU 31 in this embodiment continuously and repeatedlyperforms the aforementioned speed monitoring as long as the ECU 31 is inoperation. When the ECU 31 decides through the monitoring that theincreased speed of the load torque of the vacuum pump 20 has abruptlychanged upward, the ECU 31 executes the deceleration control andmaintains the drive frequency, which has been reduced by the control,until the next timing at which it determines whether the increased speedis greater than a predetermined value.

In the case where the ECU 31 has decided that the increased speed of theload torque of the vacuum pump 20 abruptly changed upward, the ECU 31repeatedly executes the deceleration control unless a process that has apriority over the deceleration control is performed. One process thathas a priority over the deceleration control is a process of adjustingthe value of the supply current to the electric motor section 22 in sucha way as not to exceed an upper limit i2. This process will be discussedlater.

The action of the vacuum pump 20 with the above-described structure isdiscussed next referring to the time charts in FIGS. 2(a) and 2(b). Asolid line 51 in FIG. 2(a) indicates the drive frequency in the supplycurrent to the electric motor section 22. A solid line 52 in FIG. 2(b)indicates the value of the supply current to the electric motor section22 of this embodiment.

Work for wafer exchange between the process chamber 12 and the load-lockchamber 13 is carried out under a state where the load-lock chamber 13is set to the same predetermined degree of vacuum as the process chamber12 by the vacuum pump 20 and the gate valve 14 is open. At this time,the gate valve 15 and the second valve 19 are closed.

Work for wafer exchange between the load-lock chamber 13 and the outerspace of the semiconductor production apparatus 11 is carried out undera state where, with the gate valves 14 and 15 closed, the second valve19 is opened to set the load-lock chamber 13 to the same pressure asthat of the exterior space (atmospheric pressure) and the gate valve 15is then opened. At this time, the first valve 17 is closed.

At the time the load-lock chamber 13 is set to a predetermined degree ofvacuum by the vacuum pump 20 after a wafer is loaded into the load-lockchamber 13 for example, the first valve 17 is opened with the vacuumpump 20 or the electric motor section 22 driven, thereby startingevacuation of the load-lock chamber 13. Time t1 in FIGS. 2(a) and 2(b)indicates the timing at which the first valve 17 is opened, and untilwhich the ECU 31 has driven the electric motor section 22 with the drivefrequency fmax on the high-speed side of the rotational speed of theelectric motor section 22.

Before time t1, the first valve 17 is closed so that the pressure loadof the vacuum pump 20 associated with the evacuation is nearly zero andthe supply current to the electric motor section 22 reaches a minimumvalue i1.

As the first valve 17 is opened at time t1, the gas in the load-lockchamber 13 under atmospheric pressure is rapidly led into the pumpmechanism section 21, thus quickly increasing the pressure load of thevacuum pump 20. Accordingly, the output torque of the electric motorsection 22 or the load torque of the vacuum pump 20 rises. That is, thecurrent value increases at time t1 in FIG. 2(b). At this time, theincreased speed of the current value or the increased speed of the loadtorque of the vacuum pump 20 changes upward from zero to a non-zeroincreased speed. That is, as the current value is constant before timet1, the increased speed of the current value is zero.

The ECU 31 computes the increased speed of the load torque of the vacuumpump 20 from the detected information from the current detector 32. Whenthe ECU 31 determines that the increased speed is greater than apredetermined value, the ECU 31 decides that an abrupt upward change hasoccurred in the increased speed of the load torque of the vacuum pump20. Based on the decision, the ECU 31 reduces the rotational speed ofthe electric motor section 22 to decrease the increased speed of theelectric motor section 22 to a predetermined target value, for example,the increased speed of the load torque corresponding to a straight line61 indicated by the one-dot chain line in FIG. 2(b). In other words, theECU 31 executes deceleration control on the electric motor section 22.

At this time, the ECU 31 repeatedly executes the deceleration control togradually reduce the drive frequency in the supply current to theelectric motor section 22. The gradual reduction gradually lowers therotational speed of the electric motor section 22. That is, the drivefrequency is gradually reduced from the drive frequency fmax by the ECU31 starting at time t1.

The reduction in drive frequency lowers the rotational speed of theelectric motor section 22. The reduction in rotational speed suppressesthe tendency of the pressure load of the vacuum pump 20 to increase.This reduces the increased speed of the load torque of the vacuum pump20.

The ECU 31 adjusts the drive frequency in such a way that the value ofthe supply current to the electric motor section 22 does not exceed theupper limit i2. This adjustment is carried out by priority over thedeceleration control. That is, when deciding that the current value hasreached the upper limit i2, the ECU 31 rapidly reduces the drivefrequency of the electric motor section 22 from a drive frequency f1 atthat time (time t3 in this embodiment) toward the drive frequency fminon the lower-speed side.

The reduction in the rotational speed of the electric motor section 22based on the rapid decrease in drive frequency suppresses the tendencyof the output torque of the electric motor section 22 to increase, i.e.,the load torque of the vacuum pump 20, so that the torque does notexceed the upper limit corresponding to the upper limit i2. Then, theECU 31 adjusts the drive frequency to keep as high as possible therotational speed of the electric motor section 22 to accomplish highlyefficient evacuation of the load-lock chamber 13 within the range wherethe current value does not exceed the upper limit i2.

The upper limit i2 of the current value has been set to prevent thecomponents of the vacuum pump 20 from being damaged by the output torqueof the electric motor or the load torque of the vacuum pump 20 frombecoming excessively large.

When the pressure load of the vacuum pump 20 decreases due to thedepressurization of the load-lock chamber 13 by the vacuum pump 20, theECU 31 increases the drive frequency toward the drive frequency fmax tomake the rotational speed of the electric motor section 22 as high aspossible (between time t4 and time t5) within the range where thecurrent value does not exceed the upper limit i2. At this time, thepressure load of the vacuum pump 20 is decreased although the drivefrequency is increased so that the load torque (i.e., the current value)of the vacuum pump 20 shows a tendency to decrease in the embodiment.

This embodiment can provide the following advantages.

(1) The ECU 31 performs deceleration control to decrease the rotationalspeed of the electric motor section 22 when an increase in load torqueof the vacuum pump 20 abruptly changes upward. This can reduce theincreased speed at the time the load torque of the vacuum pump 20 rises.It is therefore possible to reduce shocks applied to the components ofthe vacuum pump 20 when the increased speed of the load torque of thevacuum pump 20 abruptly changes upward or in the state where theincreased speed is high and continues after the upward change. Thiseliminates the need to reinforce the components of the vacuum pump 20 inorder to improve the shock resistance, thereby preventing enlargementand weight increase of the vacuum pump 20 that would otherwise beoriginated from the reinforcement.

(2) The ECU 31 computes the load torque of the vacuum pump 20 based onthe value of the supply current to the electric motor section 22. Thismakes it unnecessary to particularly provide a torque sensor or anotherdevice to detect the load torque of the vacuum pump 20. This leads tocost reduction and simplification of the structure.

(3) The ECU 31 repeatedly monitors the increased speed of the loadtorque of the vacuum pump 20 at a predetermined time interval and keepsdoing the monitoring even after it determines that the increased speedof the load torque of the vacuum pump 20 has abruptly changed upward.Accordingly, the rotational speed of the electric motor section 22 iscontrolled adequately according to a change in the increased speed ofthe load torque of the vacuum pump 20 even after the decelerationcontrol has started.

(4) When the increase in load torque of the vacuum pump 20 is greaterthan a predetermined value, the ECU 31 decides that the increased speedof the vacuum pump 20 has abruptly changed upward and executes thedeceleration control. This eliminates a process for computing adifference in the increased speed of the load torque of the vacuum pump20 as compared with the mode that compares, for example, the increasedspeed of the load torque of the vacuum pump 20 at a predetermined timeand the increased speed at a predetermined time different from theformer predetermined time. That is, the arithmetic operation in the ECU31 is made simpler to reduce the load thereon.

In the time chart in FIG. 2(b), as the pressure load associated withevacuation of the vacuum pump 20 is nearly constant (nearly zero), thevalue of the increased speed of the load torque of the vacuum pump 20before time t1 at which the rise of the load torque of the vacuum pump20 has started becomes a constant value (zero). In such a case, it ispossible to accurately determine whether the increased speed of the loadtorque has abruptly changed upward or not by merely determining whetherthe increased speed of the load torque is greater than a predeterminedvalue or not. In this case, therefore, it is possible to accuratelydetermine whether the increased speed of the load torque has abruptlychanged upward or not without calculating the difference in increasedspeed.

(5) The ECU 31 carries out the deceleration control to reduce theincreased speed in load torque of the vacuum pump 20 to a predeterminedtarget value. This controls the increased speed of the load torque ofthe vacuum pump 20 in such a way as to come closer to or seek thepredetermined target value. The control can reduce the increased speedat the rising of the load torque of the vacuum pump 20 greater than theincreased speed in the prior art.

(6) The ECU 31 controls the electric motor section 22 in such a way thatthe load torque of the vacuum pump 20 does not exceed a predeterminedupper limit or the upper limit of the load torque corresponding to theupper limit i2. Accordingly, the ECU 31 restricts the maximum value ofthe load torque that acts on the vacuum pump 20, making it possible toprevent deformation, damage or the like of the components of the vacuumpump 20 that originates from an excess load torque.

(7) The deceleration control is performed by the ECU 31 by changing thedrive frequency in the supply current to the electric motor section 22toward the low-speed side of the rotational speed of the electric motorsection 22. The change in drive frequency toward the low-speed sidereduces the rotational speed of the electric motor section 22, therebydecreasing the pressure load of the vacuum pump 20. The reduction inpressure load lowers the increased speed of the load torque of thevacuum pump 20.

(8) The electric motor section 22 is constructed by a synchronous motortype brushless DC motor. This makes it easier to enhance the durabilityof the electric motor section 22 as compared with a motor with a brush.Further, the rotational speed of the electric motor section 22 isadjusted by adjusting the drive frequency in supply current regardlessof the load torque that acts on the vacuum pump 20.

(9) The load-lock chamber 13 is the relay point at the time a work itemis exchanged between the atmospheric pressure space surrounding thesemiconductor production apparatus 11 and the process chamber 12.Therefore, the pressure in the load-lock chamber 13 is frequentlyincreased to atmospheric pressure from a predetermined degree of vacuum.That is, a rapid increase in load torque originating from a suddenincrease in pressure load of the vacuum pump 20 that evacuates theload-lock chamber 13 frequently occurs in the vacuum pump 20. It istherefore particularly effective to improve the durability of the vacuumpump 20 by using the inverter 30 that has the motor control means of theembodiment in such a mode.

The invention can also be applied in the following mode withoutdeparting from the scope of the present invention.

In the illustrated embodiment, the ECU 31 is constructed in such a waythat when the ECU 31 decides that an increased speed in load torque ofthe vacuum pump 20 is greater than a predetermined value, the ECU 31determines that the increased speed of the vacuum pump 20 has abruptlychanged upward and executes the deceleration control to reduce therotational speed of the electric motor section 22. Instead of thecontrol, the ECU 31 may compute the rate of change in the increasedspeed of the load torque of the vacuum pump 20 or the amount of changein increased speed per unit time and may execute the decelerationcontrol when deciding that the computation result is greater than apredetermined value. This modification allows the controller toaccurately grasp how much the increased speed of the load torque of thevacuum pump 20 has changed in a predetermined time even when theincreased speed of the load torque of the vacuum pump 20 before time t1is not constant.

In this case, the ECU 31 computes, for example, the difference betweenthe increased speed of the load torque at the current point of time andthe increased speed of the load torque at a predetermined time prior tothe current time. When the ECU 31 determines that the computation resultof subtracting the increased speed of the load torque at a predeterminedtime prior to the current time from the increased speed of the loadtorque at the current time, i.e., the difference in the amounts of theincreased speed is greater than a predetermined value, the ECU 31decides that an abrupt upward change has occurred in the increased speedof the load torque of the vacuum pump 20. Having made the decision, theECU 31 carries out the deceleration control to reduce the increasedspeed of the load torque of the vacuum pump 20.

The increased speed of the load torque of the vacuum pump 20 need notshow a tendency of linear increase over the entire period from the time(time t1) at which the ECU 31 has started reducing the drive frequencyto the point at which the current value of the electric motor section 22reaches the upper limit i2. For example, if the increased speed of theload torque starting at time t1 is made smaller than that in the priorart, the increased speed of the load torque may be made greater thanthat in the prior art until the current value reaches the upper limit i2thereafter. This makes the time for the current value to reach the upperlimit i2 shorter than in the prior art while reducing the increasedspeed immediately after a rise in the load torque of the vacuum pump 20has started.

The ECU 31 may execute the deceleration control to reduce the rate ofchange in increased speed of the load torque of the vacuum pump 20 (theamount of a change in increased speed per unit time) toward apredetermined target value. In this case, the predetermined target valueis, for example, the rate of change in increased speed of the loadtorque corresponding to a curve 62 indicated by the one-dot chain linein FIG. 3(b). FIG. 3(a) is a time chart showing the drive frequency inthe electric motor section 22 and FIG. 3(b) is a time chart showing thecurrent value in the electric motor section 22. A broken line 91 in FIG.3(a), like that in FIG. 2(a), indicates the drive frequency of theelectric motor in the prior art, and a broken line 92 in FIG. 3(b), likethat in FIG. 2(b), indicates the value of the current supplied to theelectric motor in the prior art.

According to the modification, the rate of change in increased speed ofthe load torque of the vacuum pump 20 is controlled in such a way as tocome closer or coincide with the predetermined target value. Thiscontrol makes the increased speed, at least at the time the load torqueof the vacuum pump 20 has started rising, smaller than the increasedspeed in the prior art. Of shocks applied to the components of thevacuum pump 20, therefore, the shock that is originated from the rate ofchange in increased speed of the load torque of the vacuum pump 20 canbe made smaller.

Monitoring the increased speed of the load torque of the vacuum pump 20by the ECU 31 may be stopped either immediately after the ECU 31 decidesthat the increased speed has abruptly changed upward or after apredetermined time elapses from the time at which the decision was made.This can reduce the burden on the ECU 31 associated with the monitoringas compared with the case where the ECU 31 continuously and repeatedlyexecutes the monitoring as long as the ECU 31 is in operation.

In this case, the number of times the deceleration control is repeatedlyexecuted by the ECU 31 may be restricted. This can permit, for example,the rotational speed of the electric motor section 22 to be more quicklyreturned to a high rotational speed that ensures the high evacuationefficiency of the vacuum pump 20, while making the shock applied to thecomponents of the vacuum pump 20 smaller at the time the load torque ofthe vacuum pump 20 rises.

If a lower limit is set for the drive frequency of the electric motorsection 22 and the electric motor section 22 is driven in such a waythat the drive frequency does not go below the lower limit, for example,the number of repetitive executions of the deceleration control shouldnot necessarily be restricted.

At the time of reducing the drive frequency of the electric motorsection 22, the drive frequency may be reduced rapidly, not gradually,toward the drive frequency fmin from the drive frequency fmax. Even inthis case, it is possible to reduce the increased speed at the time theload torque of the vacuum pump 20 rises.

The upper limit i2 of the supply current to the electric motor section22 may not be provided. That is, the maximum value of the load torque ofthe vacuum pump 20 may not be limited.

The load torque of the vacuum pump 20 may be grasped from other meansthan the value of the supply current to the electric motor section 22by, for example, providing a torque sensor to detect the load torque ofthe vacuum pump 20.

The electric motor section 22 may be constituted by a synchronous motortype brushless motor other than a brushless DC motor. Examples of thismotor are a reluctance synchronous motor, a stepping motor, an inductortype synchronous motor, a permanent magnet synchronous motor and ahysteresis synchronous motor. The electric motor section 22 may beconstituted by an inductive motor type brushless motor or a brushlessmotor different from those mentioned above. The electric motor section22 may also be constituted by a motor with a brush, such as a DC motoror a universal motor.

The electric motor section 22 may be of a type in which rotational speedcan be adjusted by adjusting the voltage value of the supply current tothe electric motor section 22. In this case, the voltage value isequivalent to a rotational speed instruction value.

Although the vacuum pump 20 is provided for the load-lock chamber 13 inthe above-described embodiment, the vacuum pump 20 may be for theprocess chamber 12. The vacuum pump 20 may be used for other apparatusesthan the semiconductor production apparatus 11 as well.

Although the electric motor section 22 is the control target in theembodiment in the case where the first valve 17 is opened from the statewhere the load-lock chamber 13 is at atmospheric pressure, the presentinvention is not limited to this particular case. For instance,deceleration control of the electric motor section 22 may be executed toreduce the increased speed of the load torque of the vacuum pump 20 whenthe electric motor section 22 is activated. In the present invention,the increased speed of the load torque of the vacuum pump 20 is notlimited only to the point at which the speed increases from the state ofzero, but may include the case where deceleration control of theelectric motor section 22 is executed to reduce the increased speed ofthe load torque even at the time the increased speed becomes greaterfrom a speed higher than zero.

1. In a controller of a vacuum pump having a pump mechanism section thatperforms evacuation to set a space to be evacuated to a predetermineddegree of vacuum, the improvement comprising an electric motor sectionfor driving said pump mechanism section, wherein, when an increase inload torque of said vacuum pump per unit time abruptly changes upward,deceleration control to decrease a rotational speed of said electricmotor section is carried out.
 2. The controller according to claim 1,wherein said load torque of said vacuum pump is calculated based on avalue of a current supplied to said electric motor section.
 3. Thecontroller according to claim 1, wherein said increase in load torque ofsaid vacuum pump per unit time is monitored repeatedly at apredetermined time interval and that monitoring is continued even afterit is determined that said increase in load torque of said vacuum pumpper unit time has increased abruptly.
 4. The controller according toclaim 1, wherein, when said increase in load torque of said vacuum pumpper unit time is greater than a predetermined value, it is determinedthat said increase in load torque of said vacuum pump per unit time hasabruptly changed upward and said deceleration control is carried out. 5.The controller according to claim 1, wherein, when a rate of change insaid increase in load torque of said vacuum pump per unit time isgreater than a predetermined value, it is determined that said increasein load torque of said vacuum pump per unit time has abruptly changedupward and said deceleration control is carried out.
 6. The controlleraccording to claim 4, wherein said deceleration control is carried outto reduce said increase in load torque of said vacuum pump per unit timeto a predetermined target value.
 7. The controller according to claim 5,wherein said deceleration control is carried out to reduce a rate ofchange in said increase in load torque of said vacuum pump per unit timeto a predetermined target value.
 8. The controller according to claim 1,wherein said electric motor section is controlled in such a way thatsaid load torque of said vacuum pump does not exceed a predeterminedupper limit.
 9. The controller according to claim 1, wherein saidelectric motor section includes a synchronous motor type or inductivemotor type brushless motor.
 10. The controller according to claim 1,wherein a load-lock chamber provided side-by-side with respect to aprocess chamber in a semiconductor production apparatus is said space tobe exhausted by said vacuum pump.
 11. The controller according to claim1, wherein said increase in load torque of said vacuum pump per unittime is monitored repeatedly at a predetermined time interval, and thatmonitoring is stopped after it is determined that said increase in loadtorque of said vacuum pump per unit time has abruptly changed upward.12. The controller according to claim 11, wherein a number of times saiddeceleration control is repeated is restricted.
 13. (canceled)
 14. Amethod for controlling evacuation of a space to predetermined degree ofvacuum, the method comprising: using an electric motor to drive a pumpmechanism to evacuate the space; monitoring the load torque of saidvacuum pump per unit time; and when the load torque abruptly changesupward, performing deceleration control to reduce the rotational speedof said electric motor.
 15. A controller of controlling evacuation aspace to a predetermined degree of vacuum, the controller comprising: apump mechanism section that performs evacuation and an electric motorsection for driving said pump mechanism section, wherein, when anincrease in load torque of said vacuum pump per unit time abruptlychanges upward, deceleration control to decrease a rotational speed ofsaid electric motor section is carried out.
 16. The controller accordingto claim 15, wherein said load torque of said vacuum pump is calculatedbased on a value of a current supplied to said electric motor section.17. The controller according to claim 15, wherein said increase in loadtorque of said vacuum pump per unit time is monitored repeatedly at apredetermined time interval and that monitoring is continued even afterit is determined that said increase in load torque of said vacuum pumpper unit time has increased abruptly.
 18. The controller according toclaim 15, wherein, when said increase in load torque of said vacuum pumpper unit time is greater than a predetermined value, it is determinedthat said increase in load torque of said vacuum pump per unit time hasabruptly changed upward and said deceleration control is carried out.19. The controller according to claim 15, wherein, when a rate of changein said increase in load torque of said vacuum pump per unit time isgreater than a predetermined value, it is determined that said increasein load torque of said vacuum pump per unit time has abruptly changedupward and said deceleration control is carried out.
 20. The controlleraccording to claim 18, wherein said deceleration control is carried outto reduce said increase in load torque of said vacuum pump per unit timeto a predetermined target value.
 21. The controller according to claim19, wherein said deceleration control is carried out to reduce a rate ofchange in said increase in load torque of said vacuum pump per unit timeto a predetermined target value.